The present invention relates to a rotary valve for controlling flow of hydraulic fluid. The valve is used to control the flow of hydraulic fluid to a power steering motor. A known power steering control valve for controlling flow of hydraulic fluid to a power steering motor includes a valve sleeve having a generally cylindrical bore therein and a generally cylindrical valve core rotatably mounted therein. Each of the core and sleeve has a plurality of lands and grooves that cooperate to regulate pressure and control flow between a hydraulic pump and a steering assist motor.
When the spool and sleeve are in a neutral position fluid is communicated generally equally to opposite chambers of the power steering motor. When the core and sleeve are relatively rotated from the neutral position, fluid flow is variably restricted. Restriction of the fluid flow causes pressurized fluid to be delivered to one of the opposite chambers of the power steering motor to cause motor actuation.
The restriction is provided by cooperation of lands on the core and sleeve which define variable flow areas or orifices. Variation in the size of a flow area, and thus the amount of restriction, is provided by end surface segments of the lands on the core and sleeve. Relative rotation between the core and sleeve cause the end surface segments to be positioned at varying distances apart. Due to a high volume of hydraulic fluid flow from a fixed displacement pump and pressure changes (drops) as the hydraulic fluid flows through the flow areas, various hydraulic noise is generated. The hydraulic noise includes noise due to cavitation of hydraulic fluid flowing through a gradually expanding flow path.